Process for curing a porous muffler preform

ABSTRACT

A process for curing a porous muffler preform defined by a plurality of glass fibers and a heat-curing thermoset or thermoplastic materials applied to the plurality of glass fibers is disclosed herein. The process includes the step of enclosing the muffler preform in a chamber. The process also includes the step of surrounding the muffler preform with steam. The process also includes the step of causing steam to enter the muffler preform from multiple directions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of applicationSer. No. 12/535,936 for a METHOD OF FORMING A MUFFLER PREFORM, filed onAug. 5, 2009, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This invention relates generally to a method and apparatus for making apreform for insertion in the cavity of a muffler.

BACKGROUND OF THE INVENTION

The exhaust system of an automobile incorporates a muffler for reducingexhaust noise from the engine. Mufflers must provide appropriatesilencing while not causing too high a pressure drop. Fiber inserts canbe positioned within the muffler to assist in sound dampening andminimizing pressure drop.

SUMMARY OF THE INVENTION

According to this invention there is provided a process for curing aporous muffler preform defined by a plurality of glass fibers andheat-curing thermoset or thermoplastic materials (i.e. binders) appliedto the plurality of glass fibers. The function of the binder is toimpart mechanical integrity to the preform so that it can be easilyinserted into a muffler. The process includes the step of enclosing themuffler preform in a chamber. The process also includes the step ofsurrounding the muffler preform with steam. The process also includesthe step of causing steam to enter the muffler preform from multipledirections.

A second process for curing a porous muffler preform defined by aplurality of glass fibers and a heat-curing thermoset or thermoplasticmaterials applied to the plurality of glass fibers is also provided. Thesecond process includes the step of enclosing the muffler preform in achamber at a first pressure. The second process also includes the stepof injecting steam into the chamber through an inlet port after theenclosing step. The steam is directed by baffling surfaces inside thechamber so as to not directly impinge the steam on the muffler preform.The second process also includes the step of causing steam to enter themuffler preform from multiple directions.

A third process for curing a porous muffler preform defined by aplurality of glass fibers and a heat-curing thermoset or thermoplasticmaterials applied to the plurality of glass fibers is also provided. Thethird process includes the step of enclosing the muffler preform at afirst temperature in a chamber at first pressure. The third process alsoincludes the step of surrounding the muffler preform after the enclosingstep with steam at a second pressure greater than atmosphere and thefirst pressure and at second temperature substantially at the boilingpoint of water (i.e. saturated steam) based on the second pressure. Thethird process also includes the step of causing steam to enter themuffler preform wherein water is condensed on the muffler preformthereby imparting heat to the binder material. The third process alsoincludes the step of venting the chamber to the atmosphere after thecondensing step such that much of the condensate on the muffler preformevaporates.

Various advantages of this invention will become apparent to thoseskilled in the art from the following detailed description of thepreferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first exemplary embodiment of theinvention with portions cut-away to reveal internal structures.

FIG. 2 is cross-section of a second exemplary embodiment of theinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Two different embodiments of the invention are shown in the Figures ofthe application. Similar features are shown in the two embodiments ofthe invention. Similar features have been numbered with a commonreference numeral and have been differentiated by an alphabetic suffix.Similar features are structured similarly, operate similarly, and/orhave the same function unless otherwise indicated by the drawings orthis specification. Furthermore, particular features of one embodimentcan replace corresponding features in the other embodiment or cansupplement the other embodiment unless otherwise indicated by thedrawings or this specification.

The embodiments of the invention disclosed below are applicable to thefabrication of an insert for a muffler. However, it is noted that theprocess steps set forth herein can be applied in other fields for porouspreforms or other products used in other operating environments. Aporous preform defined by a plurality of glass fibers and a heat-curingthermoset or thermoplastic materials applied to the plurality of glassfibers can be cured and used as a muffler insert. In the curing process,steam is caused to enter the preform from different directions and doesnot directly impinge on the preform. It is noted that the thickenedarrows in the drawings schematically represent the flow of steam. Sincethe steam does not directly impinge on the preform, the preform is notdeformed by the steam entering the chamber, but is quickly and uniformlycured without the excessive accumulation of condensation. The retainedwater is about 10% of the preform by weight.

The method disclosed herein is superior to previous methods. Forexample, it is faster, can provide for more uniform curing, and can betypically carried out at a lower temperature so there is no binderdecomposition. The method also appears to be more energy efficient.Rapid curing cycle also allows the use of fewer molds.

For example, the average cure time for a batch (e.g. 40 preforms) ofphenolic based thermoset binders can be less than one second. Thiscompares with 30 seconds to 2 minutes for a forced hot air system or asimple convective hot air system. Typically, in hot air curing systems,the temperatures utilized are high enough that the binder will start todecompose. The reason for these high temperatures is to reduce theaverage curing time. In contrast, the temperatures used in this processare just above the maximum curing rate of the binder and below thetemperature at which binder decomposition could begin. This results in ahigher quality preform with minimal binder content. The curing of thepreform with the new process is also more consistent since the steamrapidly penetrates the preform and releases most of its energy as thesteam condenses. This compares with hot air systems where the outer partof preform attains higher temperatures than the inner parts of thepreform because the porous preform is a good thermal insulator in an airenvironment. Because of the very efficient transfer of energy from thesteam to the preform and the very thermally efficient steam generatorsreadily available, the overall energy consumption of this process istypically less than that of prior art hot air systems. Because of thevery rapid curing cycle, one will typically need fewer molds for thesame process throughput than will be required for hot air processes.

Referring now to FIG. 1, in a first exemplary embodiment, a mufflerpreform 10 is retained in a perforated mold 12. The preform 10 is formedfrom a plurality of glass fibers and a heat-curing thermoset orthermoplastic materials applied to the plurality of glass fibers. Atthis point, a heat-curing thermoset material is uncured, and the glassfibers are moveable relative to one another prior to curing. Theapplication of heat to the preform 10 causes the heat-curing thermosetmaterial to cure and thereby tends to immobilize the glass fibers. Boththe thermoset and thermoplastic materials can encase the fibers as wellas bridge the fibers together. Since the binder materials tend to beless flexible than the glass fibers, simply encasing the fibers with thestiff binder materials will also tend to give structural integrity tothe preform. The bridging mechanism will probably be dominant, at leastin the case of thermoplastic materials. If a thermoplastic materials isused, the heat can allow the material to form bridges between fibers.When the binder material cools, the glass fibers will be bound together.The glass fibers can be injected into the mold 12 until the mold 12 isfilled with the desired quantity of fibers. The fibers can be sprayedwith the heat-curing thermoset or thermoplastic materials while beinginjected into the mold 12. Other means and methods can be used to insertthe fibers into the mold 12 and to apply the binder either before orafter the fibers enter the mold.

As shown by FIG. 1, the mold 12 can be perforated, including apertures14 on at least two different sides. The exemplary mold 12 includes apattern of apertures 14 arranged around an entire periphery of the mold12. In one embodiment, substantially 20% to substantially 50% of anouter surface of the mold 12 can be open to receive steam. It ispossible to achieve acceptable curing with few holes in the mold.Generally, higher porosity of the mold tends to make the mold lessmechanically durable in a manufacturing environment. However, a smallerporosity tends to increase the curing time. It is also noted that apreform without a central hole could be more in the shape of a rectanglethan a cylinder, but could be cured by an embodiment of the processdisclosed herein. FIG. 2 shows a second embodiment in which a mold 12 aincludes a first set of apertures 14 a around an outer surface 16 a anda second set of apertures 18 a around an inner surface 20 a. It is notedthat the use of a mold for retaining the preform and the configurationsof the molds 12, 12 a are relevant to the exemplary embodiments and notlimitations for every embodiment.

It is also noted that either mold 12 or 12 a can be filled with aplurality of glass fibers and a heat-curing thermoset or thermoplasticmaterials assisted by a vacuum. For example, a vacuum can be applied inthe interior cavity 22 a shown in FIG. 2 as the preform materials aredirected into the annular space between the surfaces 16 a and 20 a.Other applications of a vacuum can be applied in other moldconfigurations.

Referring again to FIG. 1, the chamber 24 can be defined by a pressurevessel 26. The mold 12 retaining the muffler preform 10 can be enclosedin a chamber 24 by placing the mold 12 in the chamber 24 and closing adoor 40 of the pressure vessel 26. After the mold 12 is enclosed in thechamber 24 the chamber 24 can be filled with steam. The muffler preformis thus surrounded with steam. When the chamber 24 is closed after themold 12 is inserted, the pressure in the chamber 24 can be a firstpressure, such as atmosphere or some other level of pressure. The steaminjected into the chamber 24 is at a second pressure that is higher thanthe first pressure. Steam is caused to enter the muffler preform 10because the muffler preform 10 is porous and because of the differentialbetween the first and second pressures. The steam can thus penetrate themuffler preform 10 and contact the heat-curing thermoset orthermoplastic materials throughout the muffler preform 10.

The steam will rapidly enter the interstices of the preform. When thesteam contacts the glass filaments in the preform, it will change statefrom the gaseous phase to the liquid phase, giving up its latent heat ofcondensation to the glass fibers. The rapid movement of the steam deepinto the preform is driven by the pressure difference between the airalready present in the preform, at atmospheric pressure, and thepressure of the steam. The steam will travel rapidly and deeply into thepreform (based upon the steam pressure) and will condense to the liquidform upon contact with the relatively colder binder-coated glassfilaments.

The steam can be injected into the chamber 24 through an inlet port 28after the enclosing step. Optionally, the steam can be directed bybaffling surfaces inside the chamber 24 so as to not directly impingethe steam on the muffler preform 10. In other words, the inlet port 28can direct the steam along an axis 30 but the steam contacts the preform10 in a direction different from the axis 30. Since the steam does notdirectly impinge the preform, the steam will be less likely to deformthe preform. It will also tend to heat the preform in a more uniformmanner than if the steam directly impinges the preform from one or aplurality of inlets. FIG. 1 shows one example in which a baffle 32 ispositioned along the axis 30 between the muffler preform 10 and theinlet port 28. The baffle 32 divides or bifurcates the flow of steam toopposite sides of the muffler preform 10.

In FIG. 1, the baffle 32 is shown diffusing the flow 360 degrees aboutthe axis 30. By the arrangement shown in FIG. 1, the baffle 32 divertsthe flow to the radial periphery of the chamber 24. In operation, thesteam will penetrate the preform 10 from all sides of the preform 10about the axis 30 for the full length of the preform along the axis 30.The steam represented by arrows 44 and 46 can penetrate the preform 10initially, followed by the steam represented by arrows 48 and 50,followed by the steam represented by arrows 52 and 54, followed by thesteam represented by arrows 56 and 58, followed by the steam representedby arrows 60 and 62, and followed by the steam represented by arrows 64and 66. The arrows 44-66 are schematic and shown to illustrate theprogression of steam from the inlet port 28, around the baffle 32, andalong the axis 30. The diffusion of steam from the inlet port 28 alongthe axis 30 will occur substantially instantaneously. Thus, theembodiment in FIG. 1 provides a process for causing steam to rapidlypenetrate the preform 10 from all sides and pass from the outside of thepreform 10 to the inside.

FIG. 2 shows several other examples by which steam can be introduced toa chamber 24 a without directly impinging on the muffler preform 10 a.Inlet ports 28 a, 28 b are directed at baffles 32 a, 32 b, respectively,having various cross-sections. The baffle 32 a is shaped such that outerbaffling surfaces 36 a and 38 a extend tangent to the mold 12 a. Thus,the flow of steam directed by surfaces 36 a and 38 a would not impingedirectly on the preform 10 a. The radially inner edge 42 a of the baffle32 b is similarly shaped to be tangent to the mold 12 a. It is alsonoted that a flat plate could be utilized placed between the inlet andthe preform to diffuse the steam.

Another inlet port 28 c can be directed at an inner surface 34 a of thepressure vessel 26 a. Thus, the pressure vessel 26 a itself can define abaffling surface. An inlet port 28 d can direct steam along an axis 30 athat does not intersect the mold 12 a or the preform 10 a. The steamemitted from the inlet port 28 d can emanate from the inlet port 28 dsuch that the steam would contact the mold 12 a prior to contacting thesurface 34 a. However, the steam emitted from the inlet port 28 d wouldnot directly impinge on the preform 10 a since the axis 30 a does notintersect the preform 10 a.

The examples set forth in FIGS. 1 and 2 demonstrate that variousembodiments can be practiced to cause steam to enter the mufflerpreforms 10, 10 a from multiple directions, including oppositedirections. Inlet ports can be arranged around the periphery of thepreform or a single inlet port can direct steam into the chamber. In anembodiment having multiple inlet ports, the inlet ports can be equallyspaced about a periphery of the preform or can be grouped together.

Referring again to FIG. 1, the muffler preform 10 can be enclosed in thechamber 24 when the muffler preform 10 is at a first temperature. Thefirst temperature can be selected as desired and may be ambienttemperature. The first temperature will be lower than the temperature ofthe steam to ensure that heat from the steam can be transferred to theheat-curing thermoset or thermoplastic materials. The chamber 24 can beat a first pressure when the door 40 of the pressure vessel 26 isclosed. The first pressure can be selected as desired and may be ambientpressure or atmospheric pressure. The first pressure will be lower thanthe pressure of the steam to ensure that the steam will fully penetratethe preform 10.

The temperature and pressure of the steam can be selected to ensurecuring, while minimizing the likelihood that condensation will remainafter the chamber 24 is vented after curing. The temperature of thesteam is normally controlled by the steam pressure. One could attach asubsequent heater to increase the temperature of the steam. Thatsolution may be more costly than simply increasing the operatingpressure of the steam generator. It is desirable to minimize the amountof condensation that remains on the preform after the curing process.The pressure of the steam can be at least eight times the first pressurein the exemplary embodiments, but could be less than eight times inother embodiments. For example, the steam can be injected into thechamber 24 at a pressure in the range of about 150 p.s.i. (10.2atmospheres) to about 190 p.s.i. (12.9 atmospheres).

Generally, higher steam pressure corresponds to higher cost, so thepressure of the steam can be selected as the minimum pressure at whichthe steam will fully and quickly penetrate the preform 10 and thetemperature of the steam is high enough that it will still cure thethermoset or allow the thermoplastic material to form bridges betweenfibers. The amount of condensation remaining on the preform can befurther reduced by reducing the pressure in the chamber belowatmospheric pressure for a brief time before the door is opened andpressure in the chamber raises/returns to atmospheric pressure. Thiswould also further decrease the temperature of the preforms making themeasier to handle when they are removed from the chamber.

Also, the minimum pressure of the steam can be selected in view of thecorresponding temperature at which water will vaporize. The boilingpoint of water is dependent on the extent of the surrounding pressure.The steam imparts almost all of its useable heat to the thermoset orthermoplastic materials by condensing, changing state from vapor toliquid. Thus, the pressure of the steam can be selected so that thesteam condensation will occur at a temperature that the thermoset orthermoplastic materials will rapidly cure. In one example, the steam canbe injected into the chamber 24 at a temperature in the range from about350° F. to about 380° F. The steam may be injected into the chamber 34as saturated steam, i.e. at the saturation temperature corresponding tothe steam pressure.

The temperature can also be selected in view of the pressure andtemperature conditions after the chamber 24 is vented and the door 40 isopen. Specifically, it can be desirable that all of the condensatevaporizes when the curing process is complete. Therefore, thetemperature of the steam can be selected so that the temperature of thecondensate resulting from curing will be at a temperature high enough tovaporize at the pressure in the chamber 24 after venting. It is notedthat the temperature of the muffler preform 10 will be raised by thesteam, increasing the likelihood of complete vaporization of thecondensate generated by curing.

An exemplary process according to an embodiment can proceed as follows.The mold 12 can be filled with a plurality of glass fibers and aheat-curing thermoset or thermoplastic materials applied to theplurality of glass fibers. The filled mold 12 can then be placed in thechamber 24 and the door 40 of the pressure vessel 26 can be closed todefine the closed chamber 24. The temperature of the mold 12, preform10, and the interior of the chamber 24 can be ambient. The pressure inthe chamber 24 can be ambient. After the pressure vessel 26 is closed,steam can be injected into the chamber 24 for a period of about 20seconds to about 120 seconds. The steam can be at a temperature in therange from about 350° F. to about 380° F. After a time within the rangeof about 120 seconds to about 150 seconds, the pressure in the chamber24 can be in the range of about 120 p.s.i. to about 190 p.s.i. The timerequired to reach the maximum pressure is mainly dependent upon thecapacity of the steam generator. In one commercial operation, a pressureof 150 psi would be reached within 20 seconds of the start ofpressurization. As the chamber is being pressurized, the interior of thepreform lags the temperature of the steam by about 15 seconds and lessthan 15° C. After reaching the maximum pressure, the time required tocure the binder or cause the binder to flow sufficiently that thepreform will have mechanical integrity when cooled is in the range ofabout 30 seconds to about 150 seconds. Generally, the lower the steamtemperature, the longer will be the time required for curing. Next, thechamber 24 can be vented and the door 40 to the pressure vessel 26 canbe opened. It can be desirable to vent the chamber 24 and open the door40 as quickly as possible so that the condensate does not experience atemperature drop, thus decreasing the likelihood of completeevaporation. In some embodiments, the chamber 24 can be vented and thedoor 40 opened in a time within the range of about 20 seconds to about40 seconds. In another embodiment, the pressure in the chamber 24 can bereduced below atmospheric to decrease the amount of moisture remainingon the preform and further cool the preform. If there is condensate inthe chamber, it can be removed before the door is opened.

The principle and mode of operation of the broader invention have beendescribed in its preferred embodiments. However, it should be noted thatthis invention may be practiced otherwise than as specificallyillustrated and described without departing from its scope.

1. A process for curing a porous muffler preform defined by a pluralityof glass fibers and a heat-curing thermoset or thermoplastic materialsapplied to the plurality of glass fibers, the process comprising thesteps of: enclosing the muffler preform in a chamber; surrounding themuffler preform with steam; and causing steam to enter the mufflerpreform from at least two directions.
 2. The process of claim 1 whereinthe enclosing step is further defined as enclosing an uncured mufflerpreform in a chamber.
 3. The process of claim 1 wherein the surroundingstep further includes surrounding the muffler preform with steam suchthat the steam concurrently enters the muffler preform from oppositedirections.
 4. A process for curing a porous muffler preform defined bya plurality of glass fibers and a heat-curing thermoset or thermoplasticmaterials applied to the plurality of glass fibers, the processcomprising the steps of: enclosing the muffler preform in a chamber at afirst pressure; and injecting steam into the chamber through an inletport after the enclosing step wherein the steam is directed by bafflingsurfaces inside the chamber so as to not directly impinge the steam onthe muffler preform.
 5. The process of claim 4 including the step ofcausing steam to enter the muffler preform concurrently from multipledirections.
 6. The process of claim 4 wherein the injecting stepincludes directing the steam along an axis intersecting the mufflerpreform and positioning a baffle along the axis between the mufflerpreform and the inlet port, wherein the baffle bifurcates the flow ofsteam to opposite sides of the muffler preform.
 7. The process of claim4 wherein the injecting step is further defined as injecting steam intothe chamber at a second pressure at least eight times the firstpressure.
 8. The process of claim 4 further comprising the step ofretaining the muffler preform in a perforated mold in the chamber,wherein the perforated mold includes apertures on at least two differentsides.
 9. The process of claim 8 wherein the perforated mold includes anouter surface exposed in the chamber and an inner surface surrounded bythe outer surface and also exposed in the chamber and wherein theinjecting step includes causing steam to enter the mold through both theinner and outer surfaces.
 10. The process of claim 4 wherein the steamis injected into the chamber at a temperature in the range from about330° F. to about 390° F.
 11. The process of claim 4 wherein the steam isinjected into the chamber at a pressure in the range of about 90 p.s.i.to about 190 p.s.i.
 12. The process of claim 4 further comprising thestep of retaining the muffler preform in a mold in the chamber.
 13. Theprocess of claim 12 in which substantially 5% to substantially 50% of anouter surface of the mold is open to receive steam.
 14. The process ofclaim 4 further comprising the steps of: causing steam to enter themuffler preform from multiple directions; raising the temperature of themuffler preform to substantially the temperature of the steam bycontacting the muffler preform with the steam; raising the pressure inthe chamber through the introduction of the steam to the chamber;condensing water on the muffler preform to impart heat to theheat-curing thermoset or thermoplastic materials; maintaining thetemperature and pressure of the steam in the chamber for the timerequired to cure the binder or cause the binder to flow sufficientlythat the preform will have mechanical integrity when cooled; and ventingthe chamber after the maintaining step.
 15. The process of claim 14wherein the venting step includes returning the pressure in the chamberto atmospheric in substantially 25 seconds after the directing step. 16.A process for curing a porous muffler preform defined by a plurality ofglass fibers and a heat-curing thermoset or thermoplastic materialsapplied to the plurality of glass fibers, the process comprising thesteps of: enclosing the muffler preform at a first temperature in achamber at first pressure; surrounding the muffler preform after theenclosing step with steam at a second pressure greater than atmosphericand the first pressure and at second temperature substantially at theboiling point of water based on the second pressure; and causing steamto enter the muffler preform wherein water is condensed on the mufflerpreform thereby imparting heat to the heat-curing thermoset orthermoplastic materials.
 17. The process of claim 16 including the stepof venting the chamber to atmosphere after the condensing step such thatsubstantially all the condensate evaporates from the muffler preform.18. The process of claim 16 wherein the venting step is further definedas venting the chamber in a time less than about twenty-five seconds.19. The process of claim 16 further comprising the step of: reducing thepressure in the chamber below atmospheric after the surrounding step.